The invention relates to a pressure measuring device, specifically a pressure transducer which transforms a pressure change being tested into a change of output signal frequency.
In the prior art, the pressure transducer of the electrical resistance strain gage type which is extensively used for measuring the internal pressure of soil and other loose solid substances, and for measuring interface pressure of reinforced concrete structures to which it is contacted, transforms the pressure change into a change of output resistance, and then into a change of electrical bridge output voltage. This type of AM transducer has the following disadvantages: low output signal amplitude, low S/N ratio, low anti-interference capability, a measured accuracy which is affected by the voltage of the power supply of the electrical bridge and by the length of the transmission cable, a zero point drift which occurs with changes of time and ambient temperature, and not being adapted for long-term operation and telemetry.
Another type of pressure transducer which is extensively used is known as a vibrating string type. It measures pressure change by transforming the pressure change tested into a change of vibration frequency of the string which is fixed between the base of the transducer and the film. It is a transducer of FM (frequency modulation) type having advantages of high stability and high anti-interference capability. Nevertheless, it has the disadvantages of low sensitivity, rather great non-linear error, it processes test data inconveniently, tested dynamic pressure waveforms are liable to be distorted, and its geometric configuration and weight are hardly in accordance with the requirements of internal pressure and dynamic pressure of solid substances like soil.